1. Field of the Invention
The present invention relates to a modulation method, a modulation apparatus, a demodulation method, a demodulation apparatus, an information recording medium, an information transmission method, and an information transmission apparatus. More particularly, it relates to a modulation method, a modulation apparatus, a demodulation method, a demodulation apparatus, an information recording medium, an information transmission method, and an information transmission apparatus suitable for modulating, demodulating, recording, and transmitting a digital information signal as an information code series which satisfies k=9 in a (1, k) run length limited (hereinafter referred to as xe2x80x9c(1, k) RLLxe2x80x9d), while limiting the repetition of a shortest run, so that the digital information signal is recorded in storage mediums such as an optical disk and magnetic disk by a recording code series to satisfy k=9 in the (1, k) RLL.
2. Description of the Related Art
As a recording modulation system for recording a series of digital information signals in recording mediums such as an optical disk and magnetic disk, (1, 7) RLL has heretofore been used frequently. However, in the (1, 7) RLL which has heretofore been used, it is difficult to suppress signal components in the vicinity of a direct current (DC). Depending on a bit pattern, a large DC component is generated, and for example, a spectrum of an information signal component is entrained in a servo signal band. In consequence, it is predicted that problems adversely influencing servo capabilities occur.
Moreover, it is known that the repetition of a shortest run, that is, 2T (T denotes a channel bit interval) in the (1, 7) RLL is disadvantageous for clock detection by a phase locked loop (PLL). In this connection, it is described in Jpn. Pat. Appln. KOKAI Publication No. 1994-195887 titled xe2x80x9cRecording Code Modulation Apparatusxe2x80x9d that a specified bit pattern is prevented from being repeated and thereby DC components are suppressed. Moreover, it is also disclosed in Jpn. Pat. Appln. KOKAI Publication No. 1998-340543 titled xe2x80x9cEncode Apparatus, Decode Apparatus, Encode Method, and Decode Methodxe2x80x9d or in Jpn. Pat. Appln. No. 1998-150280 corresponding to KOKAI Publication No. 11-346154 titled xe2x80x9cModulation Apparatus and Method, Demodulation Apparatus and Method, and Providing Mediumxe2x80x9d that redundant bits are inserted not to disturb the (1, 7) RLL rule, and thereby the DC components are suppressed. Furthermore, in Jpn. Pat. Appln. KOKAI Publication No. 1999-346154, (1, 7) RLL modulation is disclosed in which the repetition of the shortest run can be limited.
However, according to the Jpn. Pat. Appln. KOKAI Publication No. 1994-195887, the repetition of the specified pattern is reduced by means such as bit reverse and randomizing, but it is difficult to sufficiently suppress the DC components. Moreover, according to the Jpn. Pat. Appln. KOKAI Publication No. 1998-340543, as compared with the former, the DC components are largely suppressed, but all of the redundant bits cannot be DSV controlled. Furthermore, unless the redundant bits are used, it is disadvantageously impossible to perform the DSV control. On the other hand, in the Jpn. Pat. Appln. KOKAI Publication No. 1998-150280, parity numbers (parity of 1 included in a symbol) of data bits and code bits are set to be the same, and the DSV control is necessarily possible by inserting the redundant bits in the data bits. However, according to the Jpn. Pat. Appln. KOKAI Publication No. 1998-150280 or 1999-346154, the DSV control is possible by the redundant bits, but there is a problem that the DSV control cannot be performed in another section.
The present invention has been developed under the above-described circumstances. An object of the present invention is to provide a method and apparatus in which even with insertion of redundant bits, DSV control is possible in any section, k satisfies 9 in a (1, k) RLL rule, and a repetition frequency of a minimum run is limited.
To achieve the object, there is provided a modulation method comprising: referring to a plurality of coding tables including output code words corresponding to input data words, and coding table designation information in which an coding table for use in encoding a next input data word is designated, to thereby encode a four bits unit of a plurality of continuous input data words into a six bits unit of a plurality of continuous output code words; and inserting two redundant bits into each predetermined number of data words of the plurality of continuous output code words, so that a digital sum variation (DSV) control is possible, k satisfies 9 in a (1, k) run length limited (RLL) rule, and a successive repetition frequency of a minimum run is limited.
Moreover, to achieve the object, there is provided a modulation apparatus comprising: a plurality of coding tables including output code words corresponding to input data words, and coding table designation information in which an coding table for use in encoding a next input data word is designated; encoding means for referring to the plurality of coding tables, and thereby encoding a four bits unit of a plurality of continuous input data words into a six bits unit of a plurality of continuous output code words; and redundant bits inserting means for inserting two redundant bits into each predetermined number of data words of the plurality of continuous output code words, so that a digital sum variation (DSV) control is possible, k satisfies 9 in a (1, k) run length limited (RLL) rule, and a successive repetition frequency of a minimum run is limited.
Furthermore, to achieve the object, there is provided a demodulation method of demodulating the plurality of continuous output code words encoded by using the modulation method according to the first aspect of the present invention and having the two redundant bits inserted into each predetermined number of data words, into a reproduction data string, the method comprising: extracting the inserted redundant bits and restoring the plurality of continuous code words; and demodulating the plurality of continuous code words into the reproduction data string based on judgment information indicating an coding table by which a subsequent code word is encoded among the plurality of coding tables, and the subsequent code word.
Additionally, to achieve the object, there is provided a demodulation apparatus which demodulates the plurality of continuous output code words encoded by using the modulation apparatus according to the second aspect of the present invention and having the two redundant bits inserted into each predetermined number of data words, into a reproduction data string, the apparatus comprising: redundant bit extracting means for extracting the redundant bits and restoring the plurality of continuous code words; and demodulating means for demodulating the plurality of continuous code words into the reproduction data string based on judgment information indicating an coding table by which a subsequent code word is encoded among the plurality of coding tables, and the subsequent code word.
Moreover, to achieve the object, there is provided an information recording medium in at least a part of which a code word encoded by using the modulation method according to the first aspect of the present invention is recorded.
Furthermore, to achieve the object, there is provided an information recording medium in at least a part of which a code word encoded by using the modulation apparatus according to the second aspect of the present invention is recorded.
Additionally, to achieve the object, there is provided an information transmission method comprising a step of transmitting a code word encoded by using the modulation method according to the first aspect of the present invention as transmission information.
Moreover, to achieve the object, there is provided an information transmission apparatus which transmits a code word encoded by using the modulation apparatus according to the second aspect of the present invention as transmission information.
The nature, principle and utility of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.